India has approved plans for a 1,500 megawatt project at Tipaimukh on the Barak River which flows from the northeast into Bangladesh before emptying into the Bay of Bengal.
Experts warn that the dam could cause two Bangladeshi rivers -- the Surma and Kushiara in northeastern Sylhet -- to dry up.
"It will be another Farakka and cause desertification in eastern Bangladesh," said Badiul Alam Khokan, a leader of the Sylhet Division Development Action Council (SDDAC).
India commissioned the Farakka Barrage in 1974 on the Ganges river along Bangladesh's northern border to divert water to the river Hoogly to keep the Kolkata port navigable.
As a result, Bangladesh faced severe water shortages during winter until a 30-year agreement was signed in 1996 to share the flow.
The main opposition Bangladesh Nationalist Party (BNP) has urged people to join protests against the "killer dam" and to raise the issue in regional and international forums. (Reporting by Nizam Ahmed; Editing by Anis Ahmed)